This application addresses the RFA: Effectiveness of Treatment for Oral Diseases in Medically Compromised Patients (R01). Radiation therapy (RT) for head and neck (H&N) cancer has significant long-term adverse effects, including irreversible hyposalivation and xerostomia, which result in increased rates of dental caries and tooth loss. RT also impairs the ability of bone to heal, leading to a life-long risk of osteoradionecrosis (ORN), often precipitated by dental extractions. Consequently, these patients are caught in a vicious circle, being at higher risk of needing dental extractions, but with extractions to be avoided post-RT due to risk for ORN. To reduce such complications, pre-RT dental assessment is now considered a best practice. However, pre- and post-RT dental management varies widely among centers, due to lack of reliable data on which evidence-based guidelines can be based. The objectives of this prospective observational cohort study are to collect data on dental outcomes after H&N RT, to identify risk factors associated with tooth loss and restoration failure, and to conduct selected comparative effectiveness analyses among dental restorative materials (some of which have been reported to have very high failure rates in this population). The specific aims are: 1.To measure the 2-year rate of tooth loss in patients who have received a standard of care dental assessment prior to H&N RT. A multi-center longitudinal cohort study will be conducted of H&N cancer patients who are to receive high-dose RT. All subjects will receive a standard-of-care pre-RT dental assessment with detailed documentation of dental/oral status and pre-RT dental management. Tooth loss will be documented at follow- up visits every 6 months. Secondary analyses will assess risk factors for tooth loss by examining associations between oral health status variables (for example: periodontal index) prior to RT and subsequent tooth loss. 2. To measure failure rates of the most commonly used dental restorative materials in patients who have received H&N RT. Additional clinical assessments, at the pre-RT and follow-up study visits, will include documentation of date and type of restorations placed and of restoration failure or replacement. Secondary analyses will compare failure rates for the most common restorative materials, and assess risk factors for restoration failure by examining associations between variables affecting oral health status (for example: fluoride use) and subsequent restoration failure. The proposed research will provide evidence to guide decision-making for optimal management of these complex patients. This contribution will be highly significant because it will directly improve patient care and outcomes by identifying evidence-based best practices for the pre- and post-RT dental management of patients receiving H&N RT. This research will enable the long-term outcome goal of developing evidence-based guidelines for management of dental disease in these patients.